1. Field of the Invention
The present invention relates to a bubble separator. More specifically, the present invention relates to a bubble separator that is capable of suppressing remixing after bubble separation, and is particularly capable of performing bubble separation with a high bubble separation efficiency for oil used in a lubrication system for an internal combustion engine.
2. Description of the Related Art
Dry sump and wet sump systems are commonly known as modes for lubricating internal combustion engines. The dry sump system is a type in which engine oil collects in an oil tank and the engine oil is sent under pressure from the oil tank through a feed pump to lubricate respective parts of the engine. Oil that falls into an oil pan is then returned to the oil tank through a scavenger pump. The wet sump system is a type in which engine oil is intaken from the oil pan by a pump and sent under pressure to lubricate respective parts of the engine. Oil that has finished lubricating then falls of its own accord into the oil pan.
However, in the dry sump system a considerable amount of air bubbles are mixed into the oil while it is being returned to the oil tank via the scavenger pump. The bubbles contained in the oil are subsequently separated by an oil filter or the like, but there is a risk of poor lubrication due to incomplete separation.
On the other hand, in the wet sump system only a relatively small amount of air bubbles are mixed into the oil, and some bubbles are further eliminated by the pressure of the pump. As a consequence, there is little risk of poor lubrication. However, there have been calls to reduce the size of the pump in order to improve fuel consumption performance. In such case, there is a risk that poor lubrication may occur because air bubbles have not been sufficiently eliminated.
Thus, the bubble fraction of oil must be decreased regardless of whether the lubrication system of the internal combustion engine is a dry sump system or wet sump system.
Hence, in order to solve the above problem, the use of a gas-liquid separator is proposed for the lubrication system of the internal combustion engine.
Currently known gas-liquid separators include one in which a fluid mixture made of gas and liquid is introduced into a cylindrical body thereof. The fluid mixture is then separated by centrifugation into the liquid and the gas (see Patent Document 1 for an example). According to Patent Document 1, a ceiling portion is provided with a gas discharge port, and a projecting portion is also provided to prevent fluid from penetrating the vicinity thereof And because the inflow of the gas-liquid fluid mixture is delayed, separated gas gathers at the ceiling portion of the gas-liquid separator body and there is no risk of the gas remixing with the inflow of gas-liquid fluid mixture anew.
[Patent Document 1] Japanese Patent Application Publication No. JP-A-2003-265984
According to Patent Document 1, however, if the inflow amount of oil is fast, then the gas is remixed by the oil flowing in from the oil induction port and the remixed fluid is discharged from the gas discharge port. Thus, the efficiency of gas-liquid separation may be lowered. Furthermore, the gas discharge port is positioned higher than the induction port, and there is no consideration given to a case where the gas discharge port is positioned lower than the induction port.